This invention relates generally to a system for determining running speed of a machine from vibration produced by the machine, and, in particular, to an apparatus and method for determining a frequency of a vibration component that exist within a complex vibration signal taken by a transducer monitoring a machine and using the determined frequency for determining running speed of the machine.
It is well known that industrial plants typically include a small number of critical machines (e.g., gas turbines, steam turbines, and generators) in comparison with a large number of balance of plant machines (BOP machines) such as fans, blowers, valves, compressors, et cetera. A full instrumentation suite on critical machines is desirable because any malfunction of these machines brings down the operation of the plant. In contrast, plant operation is not so dependent on BOP machines and, in addition, it is not cost effective to put a full instrumentation suite on BOP machines because there is so many of them to monitor. As a result, there is typically less instrumentation put on BOP machines.
However, in all machines (including BOP machines) one of the important parameters to know is machine speed and one example of a transducer that can determine machine speed, and also provide a very important phase reference, is manufactured and sold by the assignee of this patent application, Bently Nevada, LLC of Minden, Nev., USA, under the registered trademark Keyphasor(copyright). In critical machines it is relatively easy to justify installing transducers necessary to know speed. However, in BOP machines, it is more difficult to justify the time consuming, laborious, and costly endeavor of installing the complete transducer suite which often means that seismic transducers such as a velocity or acceleration transducers are normally accepted for monitoring BOP machines while transducers necessary to know speed are often not installed.
This is problematic in that a large majority of BOP machines contain rolling element bearings which, regardless of type (ball, cylindrical, spherical, tapered or needle) generate specific vibration frequencies based on the bearing geometry, number of rolling elements and speed at which the bearing is rotating (i.e., machine speed). These bearing-related vibration frequencies, typically in the range of one (1) to seven (7) times the element passage rate (the rate at which the rolling elements pass a point on either the inner or outer bearing ring), are generated even by a new bearing, but the amplitudes are very small. As a bearing fails, these bearing-related vibration frequencies will increase in amplitude. It is also well known that roller spin vibration frequency and cage vibration frequency show up in a spectrum when there is a problem. Additionally, many rolling element bearing failures are the direct result of a rotor-related malfunction (e.g., unbalance, misalignment, or rotor instability) which show up in rotor-related vibrations normally occurring in the range of one-fourth (xc2xc) to three (3) times machine speed. Furthermore, information at very high frequencies (eight times the clement passage rate to the mega hertz region) may contain early indication of a bearing problem as well as other data concerning machinery condition (e.g., rubs, gear noise, cavitation, valve noise, et cetera). Thus, the key to observing these bearing-related vibration frequencies from seismic transducers or bearing housing, casing or structural vibration measurements used to monitor rolling element bearing-related vibration problems is to know where these frequencies are which requires knowing machine speed which typically varies under on different conditions. Thus, if the machine speed is not known it is not specifically known where to look for these bearing-related vibration frequencies obtained from seismic transducers or bearing housing, casing or structural vibration measurements. Compounding this problem is the fact that seismic signals tend to be very noisy and not knowing where to look for those bearing-related vibration frequencies in a noisy seismic signal results in poor diagnosis and thus, poor predictive maintenance.
Hence, there is a need for eliminating the time consuming, laborious, and costly endeavor of installing a complete transducer suite on BOP machines for monitoring and diagnosing the condition of rolling element bearings while improving the diagnostic capability obtained from seismic transducers or bearing housing, casing or structural vibration measurements. Particularly, there is a need for solving the problem of obtaining machine speed without increasing the number of transducers required to be installed on BOP machines for improving the predictive maintenance through the use of seismic transducers or bearing housing, casing or structural vibration measurements normally accepted for monitoring machines with rolling element bearings.
The present invention is distinguished over the known prior art in a multiplicity of ways. For one thing, one embodiment of the invention provides an apparatus and method for determining running speed of a machine from vibration measurements taken by a transducer monitoring the machine for use in, for example, correlating the machine vibrations to physical phenomena that generated them. Thus, in one aspect, the present invention eliminates the time consuming, laborious, and costly endeavor of installing a complete transducer suite on BOP machines for the monitoring and diagnostics of, for example, rolling element bearings while improving the diagnostic capability obtained from transducers or bearing housing, casing or structural vibration measurements. Hence, in one aspect the present invention solves the problem of obtaining machine speed without increasing the number of transducers required to be installed on BOP machines for improving the predictive maintenance provided by seismic transducers or bearing housing, casing or structural vibration measurements commonly accepted for monitoring machines with rolling element bearings.
In one embodiment of the invention, a method for determining running speed of a machine from a signal outputted by a transducer monitoring the machine includes the steps of sampling and digitizing the signal into a first digitized signal; digitally mixing the digitized signal with a second digitized signal having a predetermined frequency for obtaining a mixed signal comprised of a stream of inphase and quadrature components; transforming the stream of inphase and quadrature components into at least one phase value; determining a signal frequency of an unknown component contained in the first digitized signal as a function of at least the one phase per second value, and calculating machine running speed as a function of the determined signal frequency of the unknown component for use in correlating the machine measurements to physical phenomena that generated them.
In another embodiment of the invention, a method for determining running speed of a machine from a signal outputted by a transducer monitoring the machine includes the steps of sampling and digitizing the vibration signal into a first digitized signal; digitally mixing the first digitized signal with a second digitized signal having a predetermined frequency for obtaining a stream of inphase and quadrature components; transforming the stream of inphase and quadrature components into at least one rotating vector; determining the angular velocity of at least the one rotating vector, and determining machine running speed as a function of the determined angular velocity of at least the one rotating vector for use in correlating machine measurements to physical phenomena that generated them.
In another embodiment of the invention, an apparatus for determining running speed of a machine from a complex vibration signal outputted by a transducer monitoring the machine is comprised of an analog to digital converter operatively coupled to the transducer for sampling and digitizing the complex vibration signal into a digitized vibration signal; a digital multiplier operatively coupled to the analog to digital converter for digitally mixing the digitized vibration signal with a digitized signal having a predetermined frequency for obtaining a mixed signal comprised of a stream of inphase and quadrature components; a filtering means operatively coupled to the digital multiplier for filtering intervals of the stream of inphase and quadrature components for obtaining a plurality of vectors each having a phase; a processor operatively coupled to the filtering means for transforming the plurality of vectors into at least one per second (phase/sec) value; the processor determining a signal frequency of a vibration component contained in the complex vibration signal as a function of at least the one phase per second value, and the processor calculating a machine running speed as a function of the determined signal frequency for use in correlating the machine vibrations to physical phenomena that generated them.
Moreover, having thus summarized the invention, it should be apparent that numerous modifications and adaptations may be resorted to without departing from the scope and fair meaning of the present invention as set forth hereinbelow by the claims.